Wet and Dry Stormwater Ponds

A pond is a type of stormwater management facility designed to collect rainwater and pollutants and prevent downstream flooding.

  • Wet ponds always have a pool of water.

  • Dry ponds only have water after rain.

Ponds have an embankment (called a dam) to hold back water that is entering the pond. Most dams are earthen (not concrete) and are grass covered. All stormwater ponds also have a control structure that releases water at a much slower rate than the stormwater entering the pond. While water remains in the pond, pollutants have time to settle at the bottom.

Most ponds located throughout Montgomery County are stormwater management ponds, even ones that are community amenities. Ponds can have many different designs, including ponds with concrete channels, dry ponds with sand filters on the pond bottom, and ponds that provided wetland habitat around the edges.

Why are Stormwater Ponds Important?

Stormwater ponds are important stormwater management tools, because they:

  • Remove pollutants 

  • Improve health of streams and rivers

  • Help to make our waters fishable and swimmable

  • Improve the quality of the Chesapeake Bay 

As rainwater flows over hard surfaces and lawns it picks up pollutants such as sediment, trash, pesticides from lawns, nutrients from fertilizer or pet waste, and oil and grease from cars. Ponds can help to reduce this pollution from entering our waterways.

Image of a dry pond with a sand filter. A dry pond with a sand filter on the bottom.